A conventional asynchronous interference avoiding system is proposed in Japanese Patent Laid-Open No. 67169/1995.
FIG. 1 is a block diagram showing an example of the conventional asynchronous interference avoiding system. As shown in FIG. 1, this conventional system comprises: a radio channel control unit 1; radio connection devices 2, 3, 4, 5; and mobile units 6, 7, 8, 9.
The radio channel control unit 1 performs the control of exchange between a general public network or other mobile communication system and a radio channel within a system, a mobile management for the mobile units 6, 7, 8, 9, and radio management for the system. The radio connection devices 2, 3, 4, 5 perform setting/release regarding the radio channel with respect to the mobile units 6, 7, 8, 9 under the control of the radio channel control unit 1 and, at the same time, monitor the radio channel. The mobile units 6, 7, 8, 9 perform communication through the radio connection devices 2, 3, 4, 5 and the radio channel control unit 1 while moving within the system.
Setting of the radio zones 10A, 10B, 10C, 10D are carried out respectively with respect to the radio connection devices 2, 3, 4, 5.
FIG. 2 is a block diagram showing the construction of the radio connection devices 2, 3, 4, 5 shown in FIG. 1.
The radio connection devices 2, 3, 4, 5 each comprise an antenna 101X, a radio section 102, a modem 103, a frame generator/deassembler 104, a control channel control unit 105, a communication channel control unit 106, an asynchronous interference detector 107, an interface section 108, and a slot synchronizer 109.
FIG. 3 is a diagram showing the flow of the operation in the radio channel control unit 1 shown in FIG. 1. Here the operation of the radio channel control unit 1 will be explained by taking the mobile unit 6 and the radio connection device 2 as an example. It is assumed that the mobile unit 6 is in communication with the radio connection device 2 through a slot 2S with a frequency f1. A spare channel slot (in this case, a slot 4S), which is not usually used, is provided in the radio connection device 2. This spare channel slot is used to search for an idle carrier. Information about this idle carrier is loaded onto the slot 2S under communication and is informed as a notification of idle carrier information to the mobile unit 6 (in this case, frequency f2, slot 4S). As soon as the idle carrier has become unusable, search for a new idle channel is performed, followed by updating and notification.
During this period, the radio connection device 2 measures the receive level of a plurality of points in the slot 2S under communication in the asynchronous interference detector 107, and reports the results to the communication channel control unit 106. Based on the results of the measurement, the communication channel control unit 106 performs the detection of asynchronous interference. If the asynchronous interference has been detected, then switches the channel to the communication channel (frequency f2, slot 4S) which has previously been notified as idle carrier information. The mobile unit 6 detects that the communication signal, which could have been received up to this time, cannot be received, followed by switching of the channel to the previously notified communication channel (frequency f2, slot 4S). In this connection, it should be noted that, likewise, the asynchronous interference detector 107 is provided on the mobile unit 6 side and operated. In the drawing, slots 1S and 3S are shown, and the explanation of other elements is omitted.
Japanese Patent No. 2553286 discloses an asynchronous interference avoiding method which can effectively and exactly detect particularly interference caused by asynchronous interference waves from the rear of the burst frame in a desired signal wave in time sharing digital mobile radio communication and can efficiently start the interference avoiding operation.
The prior art techniques, however, had the following problems.
When the conventional asynchronous interference avoiding system is used to cope with the asynchronous interference among the radio connection devices 2, 3, 4, 5, an asynchronous interference detector is provided on terminal side, that is, the mobile units 6, 7, 8, 9. In this construction, the terminal side detects interference by means of the asynchronous interference detector, and the channel is hopped to a previously notified communication channel. On the other hand, the radio connection devices 2, 3, 4, 5 detect asynchronous interference, based on the fact that a signal from the terminal side is not received, and perform channel hopping. When the terminal side is operated by a battery, however, the unreceive of the signal from the terminal side is attributable to channel hopping due to the occurrence of interference, as well as to exhausting of the power of the battery. Therefore, disadvantageously, judging the occurrence of interference, based on the unreceive of a signal from the terminal side, is not reliable.